Limitations of Bohr's Model

Bohr's model was a triumph for hydrogen, but it had real limits. First and most seriously, it could not explain the spectral lines of any atom OTHER than hydrogen (or other single-electron, hydrogen-like ions) -- the model's mathematics simply does not extend to multi-electron atoms, where electron-electron interactions matter. Even restricted to hydrogen itself, more precise experimental study revealed that some of its spectral lines are not perfectly single, sharp lines but actually consist of several very closely spaced sub-lines (fine structure), a detail the simple Bohr model has no mechanism to produce.

Second, the model says nothing at all about why different spectral lines have different observed INTENSITIES (brightness) -- some transitions are simply much more common, and hence much brighter, than others, but Bohr's postulates give no way to predict or explain this. …